Heating or cooling of a thermal load such as a space in a building, a process, an energy distribution system, etcetera, is currently controlled and/or monitored by up to three separate instruments, including (1) a control valve which modulates the amount of flow through the heat exchange device to the demands of a thermostat (2) an adjustable restrictor valve to balance the system by restricting the maximum flow in that leg, and (3) a BTU meter to monitor the amount of energy being used.
(1) Control Valves:
The current range of control valves, modulated or regulated from the thermostat, effectively drive the actuating stem of the valve to a given height or degree of rotation. Such control valves utilize feedback systems related to the stem position and/or its movement, to indicate stem position to the thermostat, thus balancing the feedback circuit. Considerable refinements have been made with parabolic shaped plugs or triangular slots to approximate the position of the stem relative to the amount of flow, however, changes in differential pressures defeat the accuracy of these complex machined restricting shapes, the control valves being subject to changing differential pressures, or pressure dependent. Furthermore, flow is not always relative to actual BTU's pumped, dependent also on differential temperature taken across the heat exchanger, thus limiting the accuracy of the control valve further.
(2) System Balancing Valves:
The current balancing valves are simple restriction valves adjusted to restrict the maximum flow and they require accurate and time consuming setup adjustment, and an accurate flow measuring instrument, of which there are many types, but again, as the system differential pressures change because of changing loads in other parts of the fluid flow system, so the accuracy of the measurement is affected in that these restrictor balancing valves as they too are pressure dependent.
(3) BTU Meters:
The current trend in BTU measurement is a matter of measuring flow multiplied by inlet temperature less outlet temperature all times a constant and BTU meters therefore consists of a flowmeter mounted in the fluid pipe, and two temperature probes one for the supply water and the other for the return water from the heat exchanger. While quite accurate, these devices are costly, leading to the use of substitute and inaccurate compromises.
It is thus the object of the present invention to provide a more efficient and effective, as well as less costly approach to temperature and energy management in buildings, in energy distribution networks, and in process control systems wherever temperature transmission is involved.
It is a further object of the present invention to incorporate an accurate flowmeter within a control valve, to provide modulating feedback directly from this flowmeter rather than from the valve stem position. In a preferred embodiment of the invention it is a further object to provide temperature measuring taps for supply and return fluid so effectively providing all three instruments in one pressure independent control valve/balancing valve/BTU meter for little additional cost to that of a simple control valve.